Re: [PATCH v1 2/2] phy: freescale: imx8m-pcie: assert phy reset and perst in power off

[Philipp Zabel <p.zabel@pengutronix.de>]

On Fr, 2025-02-28 at 11:38 +0100, Stefan Eichenberger wrote:
> From: Stefan Eichenberger <stefan.eichenberger@toradex.com>
> 
> Ensure the PHY reset and perst is asserted during power-off to
> guarantee it is in a reset state upon repeated power-on calls. This
> resolves an issue where the PHY may not properly initialize during
> subsequent power-on cycles. Power-on will deassert the reset at the
> appropriate time after tuning the PHY parameters.
> 
> During suspend/resume cycles, we observed that the PHY PLL failed to
> lock during resume when the CPU temperature increased from 65C to 75C.
> The observed errors were:
>   phy phy-32f00000.pcie-phy.3: phy poweron failed --> -110
>   imx6q-pcie 33800000.pcie: waiting for PHY ready timeout!
>   imx6q-pcie 33800000.pcie: PM: dpm_run_callback(): genpd_resume_noirq+0x0/0x80 returns -110
>   imx6q-pcie 33800000.pcie: PM: failed to resume noirq: error -110
> 
> This resulted in a complete CPU freeze, which is resolved by ensuring
> the PHY is in reset during power-on, thus preventing PHY PLL failures.
> 
> Cc: stable@vger.kernel.org
> Fixes: 1aa97b002258 ("phy: freescale: pcie: Initialize the imx8 pcie standalone phy driver")
> Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
> ---
>  drivers/phy/freescale/phy-fsl-imx8m-pcie.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/phy/freescale/phy-fsl-imx8m-pcie.c b/drivers/phy/freescale/phy-fsl-imx8m-pcie.c
> index 00f957a42d9dc..36bef416618de 100644
> --- a/drivers/phy/freescale/phy-fsl-imx8m-pcie.c
> +++ b/drivers/phy/freescale/phy-fsl-imx8m-pcie.c
> @@ -158,6 +158,17 @@ static int imx8_pcie_phy_power_on(struct phy *phy)
>  	return ret;
>  }
>  
> +static int imx8_pcie_phy_power_off(struct phy *phy)
> +{
> +	struct imx8_pcie_phy *imx8_phy = phy_get_drvdata(phy);
> +
> +	reset_control_assert(imx8_phy->reset);
> +	if (imx8_phy->perst)

This check is not necessary, reset_control_assert(NULL) is a no-op:

> +		reset_control_assert(imx8_phy->perst);
> +
> +	return 0;
> +}

regards
Philipp